Martensitic stainless steel



United States Patent Ofiice 3,316,085 Patented Apr. 25, 1967 3,316,085 MARTENSITIC STAINLESS STEEL Willard E. Grundman and Mary E. Potter, Thornton structure and then tempered at about 1100 to 1150 F. Tampering at such temperature is desired to produce optimum resistance to stress corrosion cracking and is used with the steel of this invention to obtain therequired Township County qsslgnors to Umted states 5 minimum tensile and impact properties. Tempering at Steel Corporation, a corporation of Delaware t t f th d 1200, F d d N0 Drawing. Filed May21, 1964, Ser.No. 369,286 emperaures 0 e er of to 2 (113mm (CL the tensile strength below the minimum required value.

To 1llustrated the propertles obtalned by following the This application relates to martensitic stainless steels teachings of our invention, steels of the following composisuitable for pressure vessel applications and more par- 0 tion were made and tested as hereinafter described:

TABLE I Chemical Composition, Weight Percent Heat N0.

0 Mn P s Si Cr N1 M0 V W ticularly to martensitic stainless steels having high tensile These heats were forged at 2100 F. to l-inch diameter strength combined with good impact properties after 30 round bars and /z-inch square bars and tested as inditempering. cated in the following Table II:

For many pressure vessel applications, steels having a TABLE H minimum room temperature tensile strength of 160,000 p.s.i. combined with a Charpy V-notch impact strength Room Temperatme Tensile lmpactstrength, of 15 foot-pounds at -40 F. are required 1n the tem- P operties Chang Enema pered condition in heavy plates up to 4 inches in thick- Hem N0, ness. We have discovered that such combination of prop- Tenslle Elongatlon Reduction Room cities can be obtamed 1n martensitic stamless steel constrength, in m M 10, Temp, taining prescribed amounts of carbon, nickel, molybdenum Percent percent and vanadium. Thus the desirable combination of prop- 40 erties may be obtained in steel containing the following 1 1611000 elements within the ranges llStfid by welght percent: 7 ,5 5 .7

Percent a.

Carbon 7: 1541325 18:0 52:3

Manganese .10-.60 3 5 Silicon .20-.80 1

'1 422..- 150,000 17.0 53.0 Chromium 11.00-14.00 ype 3 gg Heat Treatment: 30 minutes at 1800 F., air cool plus g 5 5 5O tempering for 4 hours at 1100 F., air cool.

1 m As indicated by the foregoing Table II, steels of this wherein the vanadium content is in excess of .35 with z (level?) 3? i i z l f' carbon contents in excess of .15 with the balance iron er ter i b t 5 mg i and other elements in amounts which do not adversely room, empera i o y empenng or Ours a affect the properties i 1100 F. and air coolmg to room temperature. As fur- Preferably the steel should be within the following comther mdlcated b these resultskthe carbc'n and.vanadwm positional ranges by Wight percent, contents are critical to the deslred results. With carbon in excess of .l5%, the vanadium content must exceed Percent .35 The desired results can be obtained with carbon Carbcfl and vanadium increased 'above the preferred range but Manganese I .25-.60 with no advantage in results and of course with the added S1l1con .20.50 ex ense of the increased vanadium. Chromium 12.00-12.75 The published composition of Type 422 is included in N1ckel 1.752.25 Table I and its properties in Table II for comparative Molybdenum 1.40-1.60 purposes. As shown, the required properties are not ob- Vanadium .25-35 tained with the conventional AISI Type 422 which exhibits the highest strength of the standard 12% chromium Wlth the balance and f Impurltleso steels after austenitizing, air cooling and tempering in the The steel should be fillStEIlltlZEd at about 1850 F. or range of 1100 to 1150 above for at least sufficient tune to cause the steel to be While we have shown and described several specific substantially completely austenitic. Thereafter it is cooled at a sufiiciently rapid rate to transform it to a martensitic embodiments of our invention, it will be understood that these embodiments are merely for the purpose of illustra- 3 tion and description and that various other forms may be devised with the scope of our invention, as defined in the appended claims.

We claim:

1. Martensitic stainless steel characterized by a room temperature tensile strength in excess of 160,000 p.s.i. and a Charpy V-notch impact strength in excess of 15 foot-pounds at minus 40 F. after austenitizing and tempering, said steel consisting essentially of Wt. percent Carbon .10-.25 Manganese .10-.60 Silicon .20-. 80 Chromium 11.00-14.00 Nickel 1.5-2.5 Molybdenum 1.02.0 Vanadium .25.55

wherein with the carbon content in excess of .15 the vanadium content is in excess of .35 with the balance iron and residual impurties.

2. Martensitic stainless steel characterized by a room temperature tensile strength in excess of 160,000 p.s.i. and a Charpy V-notch impact strength in excess of 15 footpounds at minus F. after austenitizing and tempering, said steel consisting essentially of with the balance iron and residual impurities.

References Cited by the Examiner UNITED STATES PATENTS 1,630,448 5/1927 Oertel 128 1,787,403 12/1930 Strauss 75128 X 2,227,891 1/1941 Rose 75128 2,306,421 12/1942 Arness' 75128 X 2,695,229 11/1954 Sheridan "75l28 I-IYLAND BIZOT, Primary Examiner.

DAVID L. RECK, Examiner.

P. WEINSTEIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,316, 085 April 25, 1967 Willard E. Grundman et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 8, for "illustrated" read illustrate line 41, Table II, sixth column, line 1 thereof, for "49" read 46 column 3, line 2, for "with" read within column 4, line 6, for ".25" read .20

Signed and sealed this 21st day of November 1967.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. MARTENSITIC STAINLESS STEEL CHARACTERIZED BY A ROOM TEMPERATURE TENSILE STRENGTH IN EXCESS OF 160,000 P.S.I. AND A CHARPY V-NOTCH IMPACT STRENGTH IN EXCESS OF 15 FOOT-POUNDS AT MINUS 40*F. AFTER AUSTENITIZING AND TEMPERING, SAID STEEL CONSISTING ESSENTIALLY OF 